BRCA1/2 mutation carriers have highly elevated odds of developing HBOC, as may their first- and second- degree relatives. Guidelines suggest that BRCA1/2 testing for these young relatives should not begin before age 18 due to limited medical benefit and potential psychosocial harm. In contrast, testing for women over age 25 is recommended as standard of care. Testing for women aged 18-25 presents a clinical dilemma. Testing at this young age could offer the advantage of providing definitive genetic risk information, allowing the opportunity to take a proactive stance to life planning. However, risk management strategies come with distinct disadvantages at this age. These include an increase of breast cancer risk associated with mammography in carriers prior to age 30. Young women face these advantages and disadvantages with limited decision making experience and decision processes that are more prone to affective biases than their older counterparts. Our ongoing qualitative work with providers suggests these emotional and developmental factors make counseling these women unique and challenging. The present application addresses the clinical dilemma that faces these young women and their providers. Guided by the Theory of Genetic Vulnerability, we will leverage our cancer genetic registry and clinical research program in a mixed-methods study of women age 18-25 with a first- or second-degree relative who is a BRCA1/2 carrier. Our resources contain well-characterized data about our large cohort of women and men with a known mutation (index carrier). These data include not only data regarding age of testing, affected status, and risk management decisions, but also psychosocial data such as distress. We will combine these secondary data with new primary data collected from young female relatives to assess variables associated with their likelihood to test. In Phase I, we will use these quantitative data to assess the relationship between a young woman's cancer family history and cancer-related emotions and cognitions on her likelihood to test. We also will assess the mediational effects of index carrier's psychosocial functioning and health behaviors on this relationship. In Phase II, we will follow our quantitative work with qualitative interviews of 20 tested women and their physicians. These interviews will allow us to determine how receipt of a genetic test result affects the psychosocial tasks of development and medical care of young female HBOC relatives from the perspective of tested young women and their providers. Our work would allow for targeted approaches to patient education and counseling in this population.